Part B2: Hydropower

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Part B2 Hydropower B2.2 Hydropower system design
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B2.2 Hydropower system designTopics System
design

• Entry arrangements
• Forbays, penstock inlets
• Penstocks and surge control
• Size of the penstock, pressure forces, anchoring
  the penstock, water hammer and its control
• Exit arrangements
• draft tubes
• Turbine selection
• Force triangles, Turbine types, specific speed,
  cavitation and its prevention
• Electronics and control
• Types of generator, Turbine control, transmission

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B2.2.1 Hydropower system design Entry
arrangements Anatomy of a forebay
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B2.2.1 Hydropower system design Entry
arrangements Anatomy of a forebay
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B2.2.1 Hydropower system design Entry
arrangements Trash rack losses
Values for Kt
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B2.2.1 Hydropower system design Entry
arrangements trash racks
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B2.2.1 Hydropower system design Entry
arrangements Alternatives to trash racks
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B2.2.1 Hydropower system design Entry
arrangements Velocity into the penstock
v1
ht
p1
Energy line
v2
p2
v3
p3
Typical values for penstock velocities 2-5 m/s
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B2.2.1 Hydropower system design Entry
arrangements Entry losses into the penstock
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B2.2.1 Hydropower system design Entry
arrangements Entry losses into the penstock
Type Type Ke
Hooded 1.0
Projecting 0.8
Sharp corner 0.5
Slightly rounded 0.2
Bell mouth (rgt0.14D) 0
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B2.2.2 Hydropower system design Penstocks
Comparison of penstock materials
Material Friction loss Weight Corrosion resistance Cost Ease of Jointing Pressure resist
Ductile iron
Asbestos cement
Concrete
Wood staves
GRP
uPVC
Mild steel
HDPE
MDPE
Poor
Excellent
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B2.2.2 Hydropower system design Penstocks
Installation
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B2.2.2 Hydropower system design Penstocks
Friction losses in penstocks

• Darcys formula
• See B2.1.1

Typical penstock losses are 5-10
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B2.2.2 Hydropower system design Penstocks
Multiple penstocks
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B2.2.2 Hydropower system design Penstocks
Losses in bends
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B2.2.2 Hydropower system design Penstocks
Losses in bends
r/D Kb
1 0.6
2 0.5
3 0.4
4 0.3
r
D

• For 45º use K x 0.75
• For 2 use K x 0.5

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B2.2.2 Hydropower system design Penstocks
Other Losses

• Contractions
• Valves

D1/d2 Kc
1.5 0.25
2 0.35
2.5 0.40
5 0.50
Type Kv
Spherical 0
Gate 0.1
Butterfly 0.3
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B2.2.2 Hydropower system design Penstocks
Energy lines
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B2.2.2 Hydropower system design Penstocks
Anatomy of a penstock
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B2.2.2 Hydropower system design Penstocks
Slide blocks
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B2.2.2 Hydropower system design Penstocks
Thermal expansion
Fe
Fe

Fe Force due to extension Ce Coefficient of
extension DT Change in temperature E Youngs
modulus D Penstock diameter t Wall thickness
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B2.2.2 Hydropower system design Penstocks
Expansion joints
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B2.2.2 Hydropower system design Penstocks
Forces on bends
F

Hydrostatic
r fluid density g gravity h total head A
penstock area Q discharge v velocity
Velocity
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B2.2.2 Hydropower system design Penstocks Bends
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B2.2.2 Hydropower system design Penstocks
Forces on bends Thrust blocks
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B2.2.2 Hydropower system design Penstocks
Anatomy of a penstock
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B2.2.2 Hydropower system design Penstocks
Water hammer
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B2.2.3 Hydropower system design Penstocks
Water hammer

Tc critical time (s) L pipe length
(m) Cp speed of sound in the pipe Cw speed
of sound in water(1420m s-1) G bulk density
of water(2GPa) E Youngs modulus D diameter
of the pipe (m) t wall thickness
(m) Dh additional pressure due to water hammer
(m of water) g gravity Dv Change in flow
velocity (m s-1)
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B2.2.2 Hydropower system design Penstocks
Water hammer Dealing with it
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B2.2.2 Hydropower system design Penstocks
Water hammer Dealing with it Surge tanks
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B2.2.2 Hydropower system design Penstocks
Getting it wrong
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B2.2.3 Hydropower system design Draft tubes
Parallel sided
Tapered

• Allows turbine to be set above water level but
  uses vacuum pressure on underside to increase
  effective head

• Recovers part of the velocity head by diffusion
  action

Limited by the vapour pressure of water
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B2.2.3 Hydropower system design Draft tubes
Exercise

• Using Bernoulli's equation and mass continuity,
  show how a tapered turbine regains velocity head
  and converts it to pressure reduction at the
  turbine

p1 v1
p2 v2
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B2.2.3 Hydropower system design Draft tubes
configurations
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B2.2.3 Hydropower system design Draft tubes
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B2.2.3 Hydropower system design Draft tubes
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